1. Field of the Invention
The present invention relates to a connection scheme for a host or the like to multiple storage devices via an optical link, and in particular to an optical connection scheme or an optical wiring scheme for realizing multiplexing/redundancy by utilizing branches of an optical link and the unidirectionality of the optical link.
2. Description of Related Art
At present, a scheme using an optical link that has attracted attention is a scheme for a connection between a host, such as a CPU and a storage device such as memory. System reliability (RAS) is important for servers, and recently even for personal computers. A system configuration of storage devices, such as memories, including those based on ECC (Error Correcting Code) and other RAIDs such as RAID for mirroring (RAID 1), are prepared to support multiplexing or redundancy thereby.
From a host, such as a CPU, a data read command or a data write command is given to storage devices such as memories. In general, when processing in accordance with the commands is executed, an input/output (IO or I/O) controller included in the storage devices or externally attached to the storage devices is used. That is, the IO controller is responsible for determining how the command given from the host is to be interpreted and how the storage device is to be operated.
In the case where a fault occurs (generally, unexpectedly) at any position among the multiple storage devices, an operation of recovering the fault is performed by using multiplexed/redundant fault tolerance. In this recovery operation, the IO controller is generally responsible for this role. In the case of RAID, a part called a RAID controller is responsible for the role, and the operation can be called “rebuild of data” because of the purpose of the recovery operation. Therefore, it is conceivable that efforts will be made to enhance the functions of this IO controller. However, in a situation in which multiple storage devices are connected by electrical wiring or electrical links, the shortening of recovery time is restricted.
The following patent literatures will be described below as they relate to the present invention:    Patent Literature 1: Japanese Published Unexamined Patent Application No. 2008-217727    Patent Literature 2: Japanese Published Unexamined Patent Application No. 2001-166177    Patent Literature 3: Japanese Published Unexamined Patent Application No. H11-6936
In Patent Literature 1, the copying speed of a copying operation between memory devices in a memory mirroring configuration is changed. However, since the change is on the assumption of electrical connection, the burden on a memory control apparatus or a mirroring control apparatus becomes complicated.
Patent Literature 2 describes a branching apparatus for branching an inputted optical signal. This literature demonstrates a general technical knowledge of the branching of light.
Patent Literature 3 relates to a method for manufacturing an optical fiber coupler (2×2 optical fiber coupler), and shows a general technical level of enabling such manufacture and describes an optical communication system using the optical fiber coupler. However, the terminal part of one end of the 2×2 optical fiber coupler is assumed to be an unnecessary port, and the unnecessary port is not utilized. This 2×2 optical fiber coupler can be called an X-type coupler because of the characteristics of its external appearance.